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Herbicide-Resistant Sunflowers Have Roots in ARS
Research By Jan
Suszkiw January 3, 2005
HA 245 and RHA 426 sound like the names of super-secret spy planes.
The truth is more mundane, though no less important to sunflower growers: HA
245 and RHA 426 are strains of sunflower germplasm that have given rise to the
oilseed crop's first herbicide-resistant cultivars.
Agricultural Research Service
Miller developed the germplasm by crossing cultivated sunflower with the
weedy relative Helianthus annuus. He began the crosses in 1998 after
learning of weed physiologist Kassim Al-Khatib's research findings. In studies
at Kansas State University, Al-Khatib showed
that some H. annuus specimens could withstand being sprayed with the
postemergence herbicide imazamox.
That observation generated considerable excitement; transferring such
resistance into cultivated sunflower could enable growers to spray
weed-infested fields without killing their crop in the process, according to
Miller, at the ARS
River Valley Agricultural Research Center in Fargo, ND.
Miller germinated the seeds of 300 H. annuus specimens from
Al-Khatib's collection, and then sprayed the young plants with herbicide to
identify the hardiest survivors. From 28 candidates, he chose six to cross with
cultivated sunflowers, producing five generations of crossbred progeny in one
year. Backcrossing eliminated unwanted traits like multiple flower heads. Each
time, Miller used embryo rescue, a technique for side-stepping fertilized
seed's lengthy dormancy stage.
In 2002, Miller and colleagues' hard work paid off with the public
release of HA 245 and RHA 426 as breeding stock that commercial seed companies
could use to produce farmer-ready cultivars. Those cultivars, known as
Clearfield sunflowers, debuted in 2003, with further releases made in 2004.
Clearfield sunflowers' herbicide resistance should be especially
useful in drought-prone regions where fields are left unplowed, a conservation
practice that can give dominant weed species a chance to sprout and cause
problems later on, according to Miller.
more about the research in the January 2005 issue of Agricultural
ARS is the U.S. Department of
Agriculture's chief scientific research agency.